Low comonomer content ethylene-acrylate polymers in stretch/cling films

ABSTRACT

A thermoplastic film is provided which is especially suited for use in stretch/cling applications such as, for example, the bundling, packaging and unitizing of foods and other goods. The film comprises a cling layer comprising (i) a non-cling polymer of at least ethylene and acrylate or vinyl acetate, blended with (ii) a compatible, non-migratory tackifier. The film may further comprise a non-cling layer comprising a polyolefin essentially free of tackifier, with or without an anticling (slip and/or antiblock) additive. Preferred polyolefins include linear low density polyethylene and polypropylene.

This application is a continuation-in-part of U.S. Ser. No. 123,002,filed Nov. 19,1987 now abandoned as of Mar. 12, 1991.

FIELD OF THE INVENTION

The present invention relates generally to thermoplastic films and, moreparticularly, to thermoplastic films having properties making themespecially well suited for use as stretch/cling wraps in variousbundling, packaging and palletizing operations.

BACKGROUND OF THE INVENTION

Stretch/cling films have found utility in a wide variety of fieldsincluding the bundling and packaging of food and other goods. Oneapplication of particular, but not limiting, interest to the presentinvention is in the bundling of goods for shipping and storage such as,for example, the bundling of large rolls of carpet, fabric or the likefor shipping from the manufacturer to a retail outlet. An importantsubset of these bundling applications is in the containment andunitizing of pallet loads.

The load of a pallet may be unitized or "bundled" by stretch-wrapping afilm several times around the articles to be palletized. There exist avariety of stretch-wrapping techniques, two of which are commonlyemployed. In one technique, the loaded pallet is placed on a rotatingturntable and the end of a continuous roll of film attached to the load.As the turntable rotates, the film is continuously wrapped around thepallet and load. Tension is applied to the film roll to cause the filmto stretch as it is applied.

Because the film is in a stretched condition, it is placed underconsiderable tension and will have a tendency to return to its original,unstretched state. This tension can cause the film to unravel from thewrapped pallet, thereby jeopardizing the integrity of the unitized load.It is desirable, therefore, that the film have cling properties toprevent unraveling of the film from the pallet.

To impart cling properties to, or improve the cling properties of, aparticular film, a number of well-known tackifying additives have beenutilized. Common tackifying additives include polybutenes, terpeneresins, alkali metal and glycerol stearates and oleates and hydrogenatedrosins and rosin esters. The cling properties of a film can also bemodified by the well-known physical process referred to as coronadischarge.

The use of tackifying additives ordinarily is not desirable. Whiletackification is known in the art to enhance cling in an olefin clingfilm relative to an untackified film, this property improvement is nottypically seen in the stretched film, and cling can becomeunsatisfactory when the film is stretched. Furthermore, the tackifiermay present blending difficulties during film manufacture, adverselyaffect optical properties of the film and enhance surface migration ofthe additive. Such migration can damage the wrapped goods and has beenknown to cause the collapse and/or telescoping of rolls.

While inner surface cling in such film wraps is desirable, outer surfacecling may be detrimental to the integrity of the load. Cling betweenadjacent wrapped pallets may cause tearing or puncturing of or otherdamage to the wrap as the pallets are transported. For this reason, itis desirable for the film to have slip or at least non-cling propertieson its "outer" side to prevent this interpallet cling. Slip is definedin terms of coefficient of friction. In other words, it is desirablethat the "outer" side of the film have a low coefficient of friction incontact with another object, particularly another like film. As withcling, slip can be imparted to the film or improved through the use ofvarious well-known slip and/or antiblock additives including silicas,silicates, diatomaceous earths, talcs and various lubricants. Underhighly stretched conditions, however, the coefficient of friction in thefilms tends to increase and even the slip additives may not provide thedesired slip properties.

The tension in the stretched film may also cause the film to be moresusceptible to punctures and tears. It is, therefore, also desirable forthe film, as a whole, to have good stretch, tensile, puncture resistanceand tear resistance properties.

Additionally, thermal stability of the various film components isimportant for the recycling of edge trim and film scrap generated in thevarious film production processes.

A wide variety of thermoplastic polymers such as, for example, polyvinylchloride, polyethylene, polypropylene and various polymers of ethyleneand other comonomers, most notably vinyl acetate, have been used asstretch/cling films. These materials standing alone, however, sufferfrom a number of shortcomings. Most cannot be stretched to a greatextent without adversely affecting their slip, tensile, tear resistanceand puncture resistance properties. For the particular case ofethylene-vinyl acetate polymers, thermal stability becomes a problem onthe reprocessing of trim and scrap.

More recently, the use of multilayer films has gained popularity. With amultilayer film, one can obtain a stretch/cling wrap having clingproperties on one side and slip properties on the other side. Forexample, U.S. Pat. No. 4,518,654 discloses a multilayer film having anA/B construction wherein the A side has cling characteristics and the Bside has slip characteristics. In the aforementioned patent, the A sideis said to comprise a polyethylene or an ethylene-monoolefin polymer,preferably linear low density polyethylene (LLDPE). To provide the LLDPEwith the desired cling properties, a tackifying agent such aspolyisobutylene (PIB), which migrates to the film surface or "blooms,"is added to the polymer. The B side is said to comprise a low densitypolyethylene (LDPE) with an anticling additive added to impart thedesired slip properties to the LDPE. This patent is hereby incorporatedby reference herein for all purposes as if fully set forth.

Other multilayer films comprising layers of the various aforementionedstretch/cling materials are disclosed in U.S. Pat. Nos. 3,508,944,3,748,962, 3,817,821, 4,022,646, 4,082,877, 4,147,827, 4,189,420,4,194,039, 4,303,710, 4,399,180, 4,364,981, 4,418,114, 4,425,268,4,436,788, 4,504,434, 4,588,650 and 4,671,987; U.K. patent applicationNo. 2,123,747; French Pat. No. 2,031,801; and European patentapplication No. 0,198,091, all of which are also incorporated byreference herein for all purposes. These multilayer films are generallyproduced by one of a number of well-known coextrusion processes alsodisclosed in the aforementioned incorporated references.

Many of the multilayer films, however, still suffer from shortcomingspossessed by their individual layers. For instance, most do not possessdesired cling properties, and have reduced cling when in a highlystretched state. Others do not possess a desirable combination ofstretch, tensile, tear resistance, puncture resistance, optical andthermal stability properties.

In European patent application No. 0,317,166 and U.S. Ser. No. 123,002now abandoned, filed Nov. 19, 1987, both of which are herebyincorporated herein by reference, there is described a stretch/clingfilm having a cling layer of ethylene-acrylate copolymer. The filmpreferably avoids the use of a tackifying additive.

Hot melt adhesives, containing a blend of (a) high density polyethyleneor isotactic polypropylene, (b) a copolymer of ethylene and an alkylester of acrylic or methacrylic acid or vinyl acetate, (c) an ionomerresin and (d) a tackifier such as a terpene resin or a glyceryl ester ofa rosin acid, are described in Karim et al U.S. Pat. Nos. 4,337,298 and4,367,113.

SUMMARY OF INVENTION

The present invention resides in part in the discovery of a tackifiedthermoplastic film. Broadly, the present invention provides astretch/wrap thermoplastic film comprising a cling layer and a secondpolymer layer adjacent the cling layer. The cling layer consistsessentially of (i) a non-cling polymer of two or more monomers, whereina first monomer comprises ethylene and a second monomer comprises anacrylate or vinyl acetate, and (ii) a compatible tackifier blendedtherewith, wherein the blend has a glass transition temperature of about0° C. or less. Miscibility of tackifier and polymer in the presentinvention surprisingly imparts cling properties to the cling layer andallows the use of relatively economical low-comonomer-content, non-clingpolymer in the cling layer. In addition, by careful selection of thetackifier, optical and other properties of the cling layer blend,relative to cling polymers of higher acrylate content, are not adverselyaffected. Cling can be readily controlled over a wide range by selectingtackifier type and amount.

The present invention further provides a multilayer stretch/cling filmhaving excellent cling properties on one side and excellent slipproperties on an opposite side.

Still further, the present invention provides a multilayer stretch/clingfilm which, as a whole, possesses desirable stretch, tensile strength,puncture resistance, tear resistance, optical and thermal stabilityproperties.

The present invention also provides a method for producing athermoplastic film having a cling layer opposite a second layer. Themethod comprises the step of coextruding into a film a polymer-tackifierblend having cling properties as an outer cling layer, with a secondlayer. The blend consists essentially of (i) a non-cling polymer of twoor more monomers, wherein a first monomer comprises ethylene and asecond monomer comprises an acrylate or vinyl acetate, and (ii) acompatible tackifier blended therewith, wherein the blend has a glasstransition temperature of about 0° C. or less.

Finally, the present invention provides a process for using suchstretch/cling film to bundle, package or unitize an article or aplurality of articles, and an article or plurality of articles sobundled, packaged or unitized.

In accordance with the present invention, there is provided athermoplastic film which comprises, in its overall concept, a clinglayer comprising a non-cling polymer of two or more monomers and acompatible tackifier intimately blended therewith. A first monomercomprises ethylene and a second monomer comprises an acrylate or vinylacetate. Such polymer shall generally be referred to as anethylene-acrylate (or EA) polymer.

The blend preferably has sufficient cling for utility as the cling layerin a stretch/cling film. More particularly, the EA polymer preferablycomprises an acrylate or vinyl acetate content of between about 1% toabout 30%, more preferably between about 5% to about 24%, mostpreferably between about 10% to about 20%, by weight based upon theweight of the EA polymer. The tackifying additive preferably comprisesfrom about 1% to about 30%, more preferably from about 5% to about 15%,by weight of the cling layer. The tackifier is preferably non-migratory,i.e. it is essentially retained in the cling layer, and when the secondlayer is a non-cling and/or core layer(s), such layer(s) is preferablyessentially free of the tackifier.

The thermoplastic film may further comprise a second cling layeropposite the first cling layer, but preferably comprises a non-clinglayer, more preferably a slip layer, opposite the cling layer, thenon-cling or slip layer comprising any suitable thermoplastic materialsuch as, for example, polyethylene (including high density, low densityand linear low density polyethylenes), polypropylene, etc. Particularlypreferred is polypropylene. The non-cling side should, of course, beessentially free of the tackifier from the cling layer so that thenon-cling layer retains its noncling characteristics. In addition, thenon-cling side may include one or more well-known anticling (slip and/orantiblock) additives, but the non-cling layer is preferably essentiallyfree of such anticling additives.

The thermoplastic film of the invention may be so constructed that alayer adjacent the first cling layer is a structural layer, and thesecond skin layer is positioned adjacent the structural layer. That is,the structural layer separates the first cling layer and the secondlayer. The second layer of the thermoplastic film may comprise a clinglayer or a non-cling layer. In either case, the second layer may be apolyolefin. Preferably, when the second layer is a cling layer, it alsocomprises a blend of a polymer of 2 or more monomers and a compatibletackifier, wherein a first monomer comprises ethylene and a secondmonomer comprises an acrylate or vinyl acetate (EA). Where the thirdlayer is a non-cling layer, it may include one or more of the well-knownanticling (slip and/or antiblock) additives.

The structural layer of the thermoplastic films having more than 2layers comprises about 5 to 95%, preferably at least about 50%, morepreferably at least about 70-80% of the weight of the film. Thestructural layer may comprise a polyolefin of suitable makeup for thepurpose to which the film is to be applied, such as, for example, linearlow density polyethylene which is common for strength and opticalproperties in unitizing applications of stretch/cling films.

The thermoplastic film of the present invention may be producedutilizing any one of a number of well-known extrusion or coextrusion (inthe case of multilayer films) equipment and processing conditions. In amultilayer film, the cling layer will preferably comprise from about 5%to about 95%, and the non-cling layer(s) will preferably comprise fromabout 95% to about 5%, of the total combined thickness of the filmlayers.

Thermoplastic films produced in accordance with the present inventionhave excellent cling properties on the cling layer and non-clingproperties, preferably slip properties, on the non-cling layer.Particularly, the use of compatible, non-migrating tackifying additivescan be utilized to impart enhanced cling properties even to a nonclingpolymer while not adversely effecting slip properties of the non-clinglayer. The present thermoplastic films, as a whole, additionally havedesirable stretch, tensile, puncture resistance and tear resistanceproperties. Further, the thermoplastic compounds used for the cling andnon-cling layers have excellent thermal stability, and edge trim scrapcan be processed without significant loss of film performance. Thiscombination of properties makes the thermoplastic films of the presentinvention especially well suited for use as stretch/cling wraps.

These and other features and advantages of the present invention will bemore readily understood by those skilled in the art from reading thefollowing detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a thermoplastic film comprised of atackified cling layer having excellent cling utilizing only a non-clingpolymer. In addition, there is provided a thermoplastic film havingexcellent cling, slip, stretch, tensile, tear resistance, punctureresistance and thermal stability properties, and none of the processing,optical and/or tackifier migration problems ordinarily associated withtackified thermoplastic films, making such film especially well suitedfor use as a stretch/cling wrap.

The thermoplastic film, in its overall concept, comprises a cling layerwhich comprises a non-cling polymer of two or more monomers and acompatible tackifier, wherein a first monomer comprises ethylene and asecond monomer comprises an acrylate or vinyl acetate. Acrylate, in thesingular, refers to both a single acrylate and combinations of differentacrylates. These polymers will generally be referred to asethylene-acrylate (or EA) polymers.

In the preferred embodiment, the EA polymer comprises anacrylate/acetate content of between about 1% to about 30%, morepreferably between about 5% to about 24% and most preferably betweenabout 10% to about 20%, by weight based upon the weight of the EApolymer. The EA polymer may have a wide range of melt indexes (MI),generally between about 0.1 to about 30, more preferably between about 1to about 15 dg/min (ASTM D-1238, Condition E).

Preferred acrylates useful in the present invention are those of thegeneral formula: ##STR1## wherein R is selected from hydrogen or ahydrocarbon group having from 1 to 22 carbon atoms, preferably an alkyl,aryl, aromatic, or olefin of the like hydrocarbon group, and wherein R'is selected from the same or different of these hydrocarbon groups.

Preferred acrylates comprise those wherein R is selected from hydrogenor an alkyl group and wherein R' is the same or different such alkylgroup. Specific examples of preferred acrylates include methyl acrylate,ethyl acrylate, propyl acrylate, n-butyl acrylate, 2-ethylhexylacrylate, decyl acrylate, octadecyl acrylate, methyl methacrylate, ethylmethacrylate, n-butyl methacrylate and the like. Of these, methylacrylate is particularly preferred.

As previously indicated, the EA polymer can comprise more than twomonomers with at least a first monomer comprising ethylene and a secondmonomer comprising one or more of the above-defined acrylates. For thecase of teror additional monomers, suitable examples include, but arenot limited to, other free radically polymerizable monomers such as, forexample, acrylic acids (i.e. acrylic, methacrylic and ethacrylic acid),other acrylates, other vinyl esters, carbon monoxide and the like. Theseadditional monomers will generally be present in small amounts, usuallyless than a total of about 10% by weight based upon the weight of the EApolymer.

In a preferred embodiment, the EA polymer has a narrow molecular weightdistribution and a reduced incidence of long chain branching which havebeen found to enhance the cling properties of the cling layer containingthe EA polymer. The narrow molecular weight distribution of the EApolymer is reflected by relatively low ratios of weight averagemolecular weight to number average molecular weight (M_(w) /M_(n)) and zaverage molecular weight to number average molecular weight (M_(z)/M_(w)). The ratio M_(w) /M_(n) is preferably less than about 3.5, morepreferably less than about 3, and especially less than about 2.5. Theratio M_(z) /M_(w) is preferably less than about 3, more preferably lessthan about 2.6, and especially less than about 2.1. A reduction in longchain branching is generally reflected in a low melt index swell ratio,i.e., the ratio of the diameter of the melt indexer extrudate (ASTMD-1238, Condition E) to the diameter of the melt indexer orifice. Themelt index swell ratio is preferably less than about 1.6, and morepreferably less than about 1.5.

Films employing the preferred EA polymer as a cling layer have beenfound to have enhanced cling, and in particular, the cling of such filmsis not as adversely affected by stretching as similar films preparedfrom EA polymers having broader molecular weight distribution and/ormore long chain branching. The film containing the EA polymer clinglayer preferably has cling of the EA "inside" layer surface against the"outside" opposite layer surface (I/O cling) at 0% stretch of at leastabout 100 grams per inch (g), more preferably at least about 200 g, andespecially at least about 250 g; and a 200% stretch I/O cling of atleast about 90 g, and more preferably at least about 100 g as determinedby the procedure described in the Examples hereinbelow. In addition,films prepared with the preferred EA polymer cling layer have enhancedoptical properties such as, for example, less haze and more gloss, butretain comparable physical properties and processability.

The EA polymer may be produced by any one of a number of well-knownprocesses such as, for example, those described in U.S. Pat. No.3,350,372, which is incorporated by reference for all purposes as iffully set forth. Generally ethylene, acrylate and, if desired, anothermonomer(s) are metered into, for example, a high pressure autoclavereactor along with any one of a number of well-known free radicalpolymerization initiators (catalysts) suitable for producing EApolymers. Particularly preferred catalysts include organic peroxidessuch as, for example, lauroyl peroxide, di-tert butyl peroxide, tertbutyl peroxide, tert butyl perpivilate and various azo compounds.Typically, the catalyst will be dissolved in a suitable organic liquidsuch as benzene, mineral oil, ISOPAR C hydrocarbon solvent or the like.Ordinarily the catalyst is used at a level of between about 50 to about20,000 ppm, more preferably between about 100 to about 250 ppm basedupon the weight of the monomers.

The tackifier can be added to the EA polymer during or after thecopolymerization reaction, or otherwise mixed in any manner obtaining anintimate blend therewith, to impart cling properties to the film. A widevariety of tackifiers are known in the art including, for example,polyisobutylenes, atactic polypropylenes, terpene resins, aliphatic andaromatic hydrocarbon resins and the like. In aforementioned applicationU.S. Ser. No. 123,002, it was noted that the EA polymers can producefilms of sufficient cling so as to not require the use of a tackifier,and that the use of such tackifiers was not desirable and preferablyavoided. However, it has been discovered that the use of a compatibletackifier in accordance with the present invention can impart clingproperties to EA polymers which otherwise have insufficient or no clingproperties. Moreover, the use of a compatible tackifier according to thepresent invention substantially avoids the disadvantages heretoforeassociated with the tackified cling polymers of the prior art, namelymigration of the tackifier to the cling surface or into an opposednon-cling layer and problems caused by such tackifier migration.

The tackifier may be selected from a number of well known tackifierssuch as, for example, rosin and its derivatives, and various hydrocarbonresins such as polyterpenes, polydienes, poly(vinyl aromatics) and thelike, provided that the tackifier is compatible with the EA polymer,i.e. miscible therewith on a molecular scale under conditions offabrication and use. In addition, the tackifier should be selected andused in such a proportion so as to obtain a cling layer of suitablecharacteristics. If an insufficient or excessive proportion of thetackifier is used, the cling properties of the cling layer may not besuitably enhanced. Also, if too much tackifier is employed, the physicalproperties of the cling layer can be adversely affected. Generally, theupper limit on the quantity of tackifier which can be employed dependsin large part on the glass transition temperature of the tackifier andits compatibility with the cling layer EA polymer. The glass transitiontemperature of the cling layer blend should not exceed about 0° C., andis preferably in the range of from about -20° C. to about 0° C. to avoidexcessive brittleness. The proportion of tackifier used desirably shouldnot exceed any upper compatibility limit, if any, or result in a glasstransition temperature of the blend which is too high so that the clinglayer is undesirably brittle. The tackifier preferably comprises fromabout 1% to about 30%, preferably from about 5% to about 15%, by weightof the cling layer.

A preferred class of compatible tackifiers includes polar tackifiershaving a glass transition temperature of from about -50° C. to about 50°C., preferably from about -10° C. to about 50° C. Preferred polartackifiers include rosin esters and hydrogenated rosin esters having anacid number from 0 to about 15 such as, for example, the methyl,glycerol, pentaerythritol and like esters of rosin and hydrogenatedrosin available under the trade designations FORAL, PENTALYN, ZONESTER,SYLVATAC, STAYBELITE, PEXALYN and the like. These tackifiers typicallyhave a Ring & Ball softening point from about 80° C. to about 105° C.FORAL 105 tackifier, a glycerol ester of hydrogenated rosin having anacid number of about 12 and a Ring & Ball softening point of about 104°C., has been found to be particularly suitable.

Another preferred class of compatible tackifiers includes amorphouspolymerized hydrocarbon resins which are liquids or semisolids at 25°C., preferably having a softening point of from about 10° C. to about25° C. Preferred amorphous hydrocarbon tackifiers include polyterpenesavailable under the trade designations ZONAREX, ZONAREZ and PICCOLYTE;polymerized C₅ diolefins available under the trade designations WINGTACKand ESCOREZ; poly(vinyl aromatics) available under the tradedesignations REGALREZ, NEVILLAC, PICCOLASTIC and KRISTALEX; and thelike.

Specific representative examples of hydrocarbon tackifiers compatiblewith EMA cling polymers containing 20 weight percent methyl acrylateinclude ZONAREZ A25, a polymer made by Arizona Chemical from terpenehydrocarbons having a softening point of about 25° C.; REGALREZ 1018, ahydrogenated styrene-based polymer, made by Hercules, having a softeningpoint of about 18° C.; WINGTACK 10, a polymer made by Goodyear fromterpenes, having a softening point of about 10° C.; ESCOREZ 2520, apolymer made by Exxon Chemical from C₅ diolefins and other reactivediolefins, having a softening point of about 20° C.; and the like.

The EA polymer/tackifier blend may, if desired, also include one or moreother well-known additives such as, for example, antioxidants,ultraviolet absorbers, antistatic agents, release agents, pigments,colorants or the like; however, this should not be considered alimitation of the present invention. The cling layer blend should,however, be essentially free of incompatible additives and otheringredients in such quantities as would substantially impair the clingor other advantageous properties of the blend.

The film of the present invention may further comprise a second clinglayer opposite this first cling layer, but preferably further comprisesa non-cling layer opposite the cling layer, with the non-cling layerpreferably comprising any suitable polyolefin or combination ofpolyolefins such as polyethylene, polypropylene, copolymers of ethyleneand propylene, and polymers obtained from ethylene and/or propylenecopolymerized with minor amounts of other olefins, particularly C₄ -C₁₂olefins. Particularly preferred is polypropylene. Suitable polypropyleneis normally solid and isotactic, i.e., greater than 90% hot heptaneinsolubles, having wide ranging melt flow rates (MFR) of from about 0.1to about 300 dg/min. As is known, such polypropylene is normallycrystalline with a density range of from about 0.89 to about 0.91 g/ccfor isotactic polypropylene. Such polypropylene and methods for makingthe same are well-known in the art, and they are readily availablecommercially. Employing polypropylene in the non-cling layer has theadded advantage of imparting abrasion resistance thereto.

Also suitable is linear low density polyethylene (LLDPE), i.e., acopolymer of ethylene with up to about 20% by weight C₃ -C₁₀ olefin(s).Especially preferred olefins include 1-butene, 1-hexene, 1-octene and4-methylpentene-1. Suitable LLDPEs include those having a densitygreater than about 0.900 g/cc, more preferably in the range of fromabout 0.900 to about 0.940 g/cc. The LLDPEs may also have a wide rangingMI, generally up to about 30 dg/min, preferably between about 0.5 toabout 10 dg/min. Such LLDPEs and methods for making the same arewell-known in the art, and they are readily available commercially.

Additionally, the non-cling layer may include one or more anticling(slip and/or antiblock) additives which may be added during or after theproduction of the polyolefin, or otherwise mixed in any manner obtainingan intimate blend therewith, to improve the slip properties of thislayer. Such additives are well-known in the art and include, forexample, silicas, silicates, diatomaceous earths, talcs and variouslubricants. These additives are preferably utilized in amounts rangingfrom about 100 ppm to about 20,000 ppm, more preferably between about500 ppm to about 10,000 ppm by weight based upon the weight of thenon-cling layer.

The non-cling layer may, if desired, also include one or more otherwell-known additives such as, for example, antioxidants, ultravioletabsorbers, antistatic agents, release agents, pigments, colorants or thelike; however, this again should not be considered as a limitation ofthe present invention.

Additionally, normal trim and scrap from the film production process canbe recycled into either the cling or non-cling layers, butpreferentially to the non-cling layer of a two-layer film or the corestructural layer of a three-layer film.

The present invention may also include one or more intermediate layersbetween the cling and non-cling layers for any one of a number ofwell-known purposes such as, for example, to modify the overall physicalproperties balance of the film, to utilize the recycle trim and scrap orto provide a barrier layer to oxygen or other gases. As just indicated,this intermediate layer may include the recycle trim and scrap, or maycomprise any other suitable polymer. The intermediate layer(s), however,is optional and should not be considered a limitation on the presentinvention.

In preparing the thermoplastic stretch/cling films of the presentinvention, any one of a number of well-known extrusion or coextrusion(in the case of multilayer films) techniques as disclosed in thepreviously incorporated references may be utilized. As preferredexamples, any of the blown or chill roll cast processes as disclosed anddescribed in those references is suitable for use in producingthermoplastic stretch/cling films in accordance with the presentinvention.

In a multilayer film, the cling layer preferably comprises between about5% to about 95%, more preferably between about 5% to about 35%, mostpreferably between about 5% to about 15% of the combined thickness ofthe film layers. Conversely, the non-cling layer(s) (including anystructural or other intermediate layer) preferably comprises betweenabout 5% to about 95%, more preferably between about 65% to about 95%,most preferably between about 85% to about 95% of the combined thicknessof the film layers.

As previously mentioned, the thermoplastic films of the presentinvention have properties making them especially well suited for use asstretch/cling films, however this use should not be considered alimitation on the present invention. For example, these films can bemade into other forms, such as a tape, by any one of a number ofwell-known cutting, slitting and/or rewinding operations. Physicalproperties including, but not limited to, tensile strength, tearstrength and elongation can be adjusted over wide ranges by altering theresin types and specifications as appropriate to meet the requirementsto a given wrapping, bundling or taping application.

For bundling, packaging and unitizing applications, the thermoplasticfilm of the present invention is stretchwrapped by any one of a numberof well-known procedures (such as those disclosed in the aforementionedincorporated references) around an article or a plurality of articlespreferably so that the cling layer faces inside (towards the article)and the non-cling layer faces outside (away from the article), althoughthis film orientation should not be considered as a limitation on theinvention. Typical of articles suitable for bundling, packaging andunitizing with the present thermoplastic film include, but are notlimited to, various foodstuffs (canned or fresh), rolls of carpet,liquid containers and various like goods normally containerized and/orpalletized for shipping, storage and/or display.

The films of the invention may also be used in surface protectionapplications and are very effective in the temporary protection of asurface during manufacturing, transportation, etc. The easily coextrudedfilms of the invention are also often less expensive than known surfaceprotection films of, e.g., LLDPE and acrylic layers. Advantageously, thefilms of the invention do not leave significant adhesive traces on thesurface to be protected and have good UV stability.

The foregoing more general discussion of this invention will be furtherexemplified by the following specific examples offered by way ofillustration and not limitation of the above-described invention.

EXAMPLES

In the following examples, property evaluations were made in accordancewith the following tests:

(1) Coefficient of Friction (COF)--ASTM D-1894.

(2) Cling--cling is reported as the force grams required to partiallypeel apart two strips of film. A first film strip is attached to a 30°inclined plane with the outside surface (slip) facing upward. A second1"×8" strip is placed on top of the first strip with the inside surface(cling) facing downward. Pressure is applied to the second strip tocause the two strips to stick together. If an evaluation of cling understretched conditions is desired, both film strips are prestretched andallowed to relax before testing. The end of the second strip at the baseof the inclined plane is attached, by clip and string, to an apparatuswhich can exert a strain at a constant rate (Instron 1130). The twostrips are then pulled apart at a crosshead speed of 10 cm/min until theaforementioned string is parallel with the base of the inclined plane.The force at this point is reported as cling.

EXAMPLES 1-6 AND COMPARATIVE EXAMPLE 1

A 20% by weight ethylene-methyl acrylate (EMA) copolymer, with an MI of6 dg/min, was blended with several different compatible tackifiers atvarying concentrations and coextruded with a PP having a density of 0.91g/cc and an MFR of 14 dg/min (commercially available from Exxon ChemicalCompany, Houston, Tex., under the trade designation PP-3014). Otherproperties of the EMA and PP are listed below in Table I.

The EMA copolymer and compatible tackifier were compounded on a 6"single screw extruder equipped with an underwater pelletizer and fiveheated zones on the screw set at 350°-400° F. with a melting temperatureof about 358° F. The film was produced by coextruding the EMA/tackifierblend and PP on a Black Clawson cast film line with two 3.5" extruders,respectively, for the EMA blend and PP layers. The EMA blend wasextruded at a melt temperature of 400° F., while the PP was extruded ata melt temperature of 450° F. The chill roll temperature was set to 80°F. and the line speed to 450 feet per minute.

The resulting film had a gauge of 0.8 mil with the EMA blend layercomprising 20% of the total film thickness. The I/O (EMA/PP) clingresults are presented below in Table I.

                                      TABLE I                                     __________________________________________________________________________           CLING LAYER COMPOSITION (wt %)                                                    ZONA-                                                                              WING-                                                                              REGAL-                                                                             ESCO-                                                                             CLING (g).sup.1                                            REZ  TACK REZ  REZ 0%   200%                                       EXAMPLE                                                                              EMA A25  10   1018 2520                                                                              Stretch                                                                            Stretch                                    __________________________________________________________________________    Comp.  100 --   --   --   --   0    0                                         1      90  10   --   --   --  250  210                                        2      85  --   15   --   --  330  210                                        3        92.5                                                                            --   7.5  --   --  240  150                                        4      85  --   --   15   --  410  340                                        5      85  --   --   --   15  420  260                                        6        92.5                                                                            --   --   --   7.5 220  160                                        __________________________________________________________________________     .sup.1 EMA to PP layer surfaces                                          

The results seen in Table I show that films in accordance with thepresent invention exhibited excellent cling properties, even uponstretching. The films furthermore retained good physical propertiesincluding extrusion processability and low coefficient of friction, i.e.slip on the coextruded polypropylene layer. Also, there was noindication of tackifier migration into the cling layer. The results alsodemonstrate the ability to tailor film cling properties by alteringtackifier type and content of the cling layer.

Many modifications and variations besides the embodiments specificallymentioned may be made in the compositions and methods described hereinwithout substantially departing from the concept of the presentinvention. Accordingly, it should be clearly understood that the form ofthe invention described herein is exemplary only, and is not intended asa limitation of the scope thereof.

What is claimed is:
 1. A stretch/wrap thermoplastic film, comprising:acling layer consisting essentially of (i) a non-cling polymer of two ormore monomers, wherein a first monomer comprises ethylene and a secondmonomer comprises an acrylate or vinyl acetate, and (ii) a compatibletackifier blended therewith, said polymer/tackifier blend having a glasstransition temperature of about 0° C. or less; and a second layeradjacent said cling layer.
 2. The film of claim 1, wherein said film hasan I/O cling of at least about 100 g.
 3. The film of claim 1, whereinsaid second monomer comprises from about 1 to about 30 percent by weightof said non-cling polymer.
 4. The film of claim 1, wherein said secondmonomer comprises from about 5 to about 24 percent by weight of saidnon-cling polymer.
 5. The film of claim 1, wherein said second monomercomprises from about 10 to about 20 percent by weight of said non-clingpolymer.
 6. The film of claim 1, wherein said second monomer comprises acompound of the formula: ##STR2## wherein R is selected from hydrogen ora hydrocarbon group having from 1 to about 22 carbon atoms and whereinR' is independently selected from a hydrocarbon group having from 1 toabout 22 carbon atoms.
 7. The film of claim 1, wherein said secondmonomer is selected from the group consisting of methyl acrylate, ethylacrylate, n-butyl acrylate and vinyl acetate.
 8. The film of claim 1,wherein said second monomer comprises methyl acrylate.
 9. The film ofclaim 1, wherein said tackifier comprises from about 1 to about 30percent by weight of said cling layer.
 10. The film of claim 1, whereinsaid tackifier comprises from about 5 to about 15 percent by weight ofsaid cling layer.
 11. The film of claim wherein said polymer/tackifierblend has a glass transition temperature between about -20° C. and about0° C.
 12. The film of claim 1, wherein said second layer is essentiallyfree of said tackifier.
 13. The film of claim 1, wherein said tackifieris nonmigratory.
 14. The film of claim 1, wherein said tackifier has aglass transition temperature of between about -50° C. and 50° C.
 15. Thefilm of claim 14, wherein said tackifier comprises a rosin ester. 16.The film of claim 1, wherein said tackifier is an amorphous polymerizedhydrocarbon resin which is liquid or semisolid at 25° C.
 17. The film ofclaim 16, wherein said tackifier is selected from the group consistingof polymerized terpenes, dienes and vinyl aromatic monomers.
 18. Thefilm of claim 1, wherein said adjacent layer is a non-cling layer ofpolyolefin.
 19. The film of claim 18, wherein said non-cling layer isessentially free of slip additive.
 20. The film of claim 18, whereinsaid non-cling layer further comprises a slip additive.
 21. The film ofclaim 1, wherein said adjacent layer comprises an intermediate layerand, opposite said cling layer, another cling layer of said blend ofsaid polymer and said tackifier.
 22. The film of claim 1, wherein saidadjacent layer comprises an intermediate structural layer and, oppositesaid cling layer, a non-cling layer.
 23. The film of claim 22, whereinsaid structural layer comprises at least about 50 percent by weight ofsaid film.
 24. The film of claim 22, wherein said non-cling layercomprises isotactic polypropylene having greater than 90% hot heptaneinsolubles and a melt flow rate of from about 0.1 to about 300 dg/min.25. The film of claim 22, wherein said non-cling layer comprises linearlow density polyethylene having a density from about 0.900 to about0.940 g/cc and a melt index between about 0.5 to about 10 dg/min.
 26. Aprocess for producing a thermoplastic film having a cling layer oppositea second layer, comprising the steps of:coextruding into a film as acling layer a polymer-tackifier blend having cling properties and aglass transition temperature of about 0° C. or less, with a secondpolyolefin layer, said blend consisting essentially of (i) a non-clingpolymer of two or more monomers, wherein a first monomer comprisesethylene and a second monomer comprises an acrylate or vinyl acetate,and (ii) a compatible tackifier; and stretching said film.
 27. Theprocess of claim 26, wherein said second layer is a structural layer andsaid coextruding step includes the coextrusion of a third layer adjacentsaid structural layer.